Synthetic filament having a cross-section based upon an ellipse

ABSTRACT

The present invention encompasses a filament having a cross-section based upon an ellipse where one side of the filament is defined by a convex-concave-convex curve. The invention also encompasses a spinneret and method for making the filament. The filament is preferably made from condensation polymers and in particular polyethylene terephthalate or other polyesters.

FIELD OF THE INVENTION

[0001] The present invention relates to the manufacture of filaments, fibers, yarns and fabrics and in particular relates to an improved synthetic filament having a unique cross-section.

BACKGROUND OF THE INVENTION

[0002] Cotton is a preferred choice among consumers for manufacturing clothing. Cotton is light in weight, absorbs moisture quickly and easily, and has a generally favorable texture (“hand”) when woven into fabrics. Chemically, cotton is formed almost entirely of fibers of pure cellulose with a typical length of about one inch, but with variations in length from about a half an inch to over two inches. Structurally, mature cotton fibers are characterized by their convolutions so that under a microscope, cotton appears as a twisted ribbon with thickened edges. The cross-section of cotton fiber can vary greatly. Generally, however, cotton fibers have an arcuate external cross-section that is on a continuum between a kidney bean shape and an exaggerated C-shape.

[0003] Although cotton has several favorable characteristics, cotton lacks certain strength characteristics and elastic memory, and thus garments formed entirely of cotton require regular laundering, pressing, and in many cases starching, between wearings by the ordinary user.

[0004] Polyester is strong, light in weight, and has excellent plastic memory characteristics. When formed into filaments, fibers and fabrics, polyester is crease-resistant, quick-drying, retains its shape in garments, is abrasion-resistant, and requires minimum care. Because of its synthetic nature, however, polyester has a generally unacceptable appearance (at least for most garment purposes) when initially formed as a filament. Accordingly, polyester filaments require texturizing in some fashion to produce acceptable characteristics of appearance, hand and comfort in yarns and fabrics.

[0005] The characteristic advantages of polyester are such, however, that efforts continue to develop polyester filament, yams and fabrics that more closely resemble those of cotton, silk or other natural fibers.

[0006] A number of chemical modifications have been carried out on polyester to obtain desirable properties. For example, U.S. Pat. Nos. 6,294,254; 6,303,739; 6,291,066; 6,322,886 and U.S. applications Ser. Nos. 09/801,853; 09/851,813; 09/444,192; 09/730,444; 09/761,446; and 09/827,441 discuss various chemical modifications incorporating polyethylene glycol and branching agents to enhance certain polyester properties. Treatment of polyester fabrics with caustic chemicals to achieve specific characteristics is also well known in the art.

[0007] Structural modifications have often been used to alter the texture of polyester fibers and fabrics. Crimping fibers is one example of physically altering a synthetic fiber to achieve a more natural-like appearance.

[0008] Varying the cross-section of polyester fibers is another technique often employed to achieve specific fiber properties. U.S. Pat. No. 4,364,996 discusses synthetic fibers having a plurality of projections that allegedly impart downy or feather-like characteristics to the fiber. U.S. Pat. No. 4,176,211 discusses polyester fibers having a C-shaped cross-section for improving the appearance of the resulting fabric. U.S. Pat. No. 5,611,981 discusses polyester fibers with deep grooves that facilitate the transport of liquid. U.S. Pat. No. 4,639,397 discusses a thick and thin filament with multiple grooves designed to mimic silk. These are just a few of the many patents that discuss filaments with non-circular cross-sections.

[0009] One problem with these non-circular filaments is that they can be difficult to produce and form into yams and fabric, depending upon their shape, and are thus more expensive than traditional circular filaments. Some of this difficulty is a function of the fiber or a function of manufacturing process or both.

[0010] For example, commercial polyester filament, fiber and yam manufacturing is an extremely complex operation that requires substantial capital investment. Most operations are set up for making circular filament because circular filaments account for the bulk of polyester filaments sold in the marketplace. Changing the cross-section of the filament can alter the physical attributes of the filament (e.g., filament strength), which can have detrimental effects in the production process (e.g., filament breakage).

[0011] Another limitation that is common to both non-circular and circular filaments is related to the spinning of fiber into yam in an open-end spinning process. Generally, as the spinning speed increases the number of “ends down” increases. “Ends down” is the term commonly used to describe broken filaments and yams. Thus, an open-end spinning process is usually governed by a balancing between throughput (i.e., spinning speed) and an acceptable number of ends down.

[0012] Accordingly, a need exists for synthetic filaments that provide some of the desirable characteristics of cotton while retaining the benefits usually associated with synthetic materials. These filaments should also be capable of being manufactured on existing equipment without increasing production disturbances. Furthermore, a need exists for a filament and fiber that exhibits fewer ends down during open end spinning operations. Stated alternatively, a need exists for filament that allows a greater spinning speed and thus increased throughput while reducing ends down as compared to yams made from circular filament.

OBJECT AND SUMMARY OF THE INVENTION

[0013] In view of the foregoing, an object of the invention is to provide a synthetic filament that mimics desirable properties of cotton such as hand while retaining the desirable properties of polyester.

[0014] A further object of the invention is to provide a synthetic filament having a cross-section that does not substantially alter the properties of yarns and fabrics made from the filament as compared to yams and fabrics made from traditional circular filaments.

[0015] A still further object of the invention is to provide a synthetic filament that spins and processes as well as or better than traditional circular filaments.

[0016] A still further object of the invention is to provide a spinneret and a method for manufacturing such a filament.

[0017] The invention accomplishes the above and other objects by providing a synthetic filament having a cross-section based upon an ellipse. The filament is defined by, among other things, a primary axis and a secondary axis, wherein the secondary axis bisects the primary axis. Likewise, the primary axis cuts the secondary axis into a first segment and a second segment where the first and second segments are of unequal length.

[0018] The primary axis defines first and second portions of the filament cross-section. An ellipitical arc, which is defined by the ends of the primary axis and the longer of the two secondary axis segments, defines the first portion of the filament cross-section.

[0019] The second portion of the filament cross-section is defined by a generally symmetrical curve defined by the ends of the primary axis and a first convex section and a second convex section separated by a concave section where the trough of the concave section is defined by the shorter of the two secondary axis segments.

[0020] In another aspect, the invention is a spinneret for spinning a synthetic filament. The spinneret has at least one opening where the opening is based upon an ellipse having a primary to secondary axes ratio of between about 1.8 to about 2.9. The opening is further defined by a perimeter having a v-shaped notch generally axially aligned with the secondary axis and extending toward the center of the ellipse.

[0021] In yet another aspect, the invention is a method of forming a synthetic filament comprising heating a fiber-forming material at or above its melting point. The material is then spun through a spinneret having at least one opening where the opening is based upon an ellipse having a primary to secondary axis ratio of between about 1.8 to about 2.9. The opening is further defined by a perimeter having a v-shaped notch generally aligned with the secondary axis wherein the angle of the notch is between 30° and 150°. In preferred embodiments the angle of the notch is between 45° and 135°, and most preferably between 80° and 130°.

BRIEF DESCRIPTION OF DRAWINGS

[0022]FIG. 1 is a schematic diagram of a spinneret according to the invention.

[0023]FIG. 2 is a schematic drawing of an exemplary production process that may be used in the practice of the invention.

[0024]FIG. 3 is a schematic drawing of a cross-section of an exemplary filament according to the invention.

[0025]FIG. 4 is a photograph of cross-sections of filaments according to the invention.

[0026]FIG. 5 is a plot of stress versus elongation for circular filaments and filaments according to the invention.

DETAILED DESCRIPTION

[0027] The invention pertains to forming synthetic filaments and fibers. As used herein, the term “fiber” broadly refers to uncut filament (e.g., partially oriented yarn (POY), flat-drawn yam, or textured yarn) and cut fiber (e.g., staple fiber). Although the term “filament” may include fibers, such as staple, that are subsequently cut from spun filament, it is generally used to refer to an extruded fiber of indefinite length. Thus, the terms “fiber” and “filament” are somewhat interchangeable and are used interchangeably herein. If a more precise meaning is required for either of these terms, such meaning will be easily understood by those of ordinary skill in the art based on the contextual use of these terms.

[0028] Likewise, the term “synthetic” as used herein generally refers to man-made polymers and particularly condensation polymers. Thus, the term “synthetic” as used herein is defined to include any polymer capable of being spun into a filament and in particular includes condensation polymers selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate, poly(trimethylene terephthalate), other polyesters, nylon 6, nylon 66 and polylactic acid (PLA).

[0029] Also included in the term “synthetic” are co-polymers consisting of condensation polymers such as polyethylene terephthalate, polybutylene terephthalate, poly(trimethylene terephthalate), other polyesters, nylon 6, nylon 66 and polylactic acid (PLA).

[0030] For ease of discussion, this detailed description is written in the context of spinning synthetic filament from polyethylene terephthalate. This contextual framework, however, should not be interpreted as limiting the scope of the invention.

[0031] Finally, it will be understood by those familiar with textile terminology that the term “spinning” is used to refer to two different processes. In one sense, the term “spinning” refers to the production of synthetic polymer filaments from a polymer melt. In its older, conventional use, the term “spinning” refers to the process of twisting a plurality of individual fibers into yarns. The use of the term “spinning” is well-understood in the art based upon the context of its use.

[0032] The synthetic polymers suitable for use in the practice of the invention may be made according to any of the methods known by those skilled in the art. Furthermore, the polymers used in the practice of the invention may also include additives commonly utilized in the production of these polymers. For example, the invention encompasses the use of polyesters that incorporate colorants and additives such as stabilizers, branching agents, static dissipaters, delusterants, etc. The methods of making all of these polymers as well as the use of additives to improve or impart specific properties are well known in the art. Accordingly, the methods of making these polymers are not discussed in detail herein.

[0033] There is one particular family of co-polymers, however, that is commonly owned by the assignee of the present application that warrants particular attention. This family comprises polyethylene glycol (PEG) modified polyester compositions that are suitable for forming fibers. Such compositions are discussed in detail in U.S. Pat Nos. 6,294,254; 6,303,739; 6,291,066; 6,322,886 and U.S. applications Ser. Nos. 09/801,853; 09/851,813; 09/444,192; 09/730,444; 09/761,446; and 09/827,441. These patents and applications describe PEG-modified copolyester fibers possessing favorable characteristics similar to those possessed by natural fibers while retaining the advantages of polyester, and that can be formed into exceptionally comfortable woven, knit, and nonwoven fabrics.

[0034] The above patents and applications set forth in great detail specifics regarding the production and use of PEG-modified polyester compositions and Applicant refers the reader to these documents for information regarding their manufacture and use. In general, however, the PEG-modified polyester compositions utilized in the practice of the present invention comprise PET, PEG having an average molecular weight less than about 5000 g/mol, a branching agent or agents, and other additives (e.g., antioxidants, etc.). Preferably the weight fraction of PEG in the fiber is between about 2 percent and about 20 percent.

[0035] The chain branching agent is a multifunctional monomer that promotes the formation of side branches of linked monomer molecules along the main polymer chain. See Odian, Principles of Polymerization, pp. 18-20 (Second Edition 1981). The chain branching agent is preferably selected from the group consisting of trifunctional, tetrafunctional, pentafunctional and hexafunctional alcohols or acids that will copolymerize with polyethylene terephthalate. As will be understood by those skilled in the art, a trifunctional branching agent has one reactive site available for branching, a tetrafunctional branching agent has two reactive sites available for branching, a pentafunctional branching agent has three reactive sites available for branching and a hexafinctional branching agent has four reactive sites available for branching.

[0036] Acceptable chain branching agents include, but are not limited to, trimesic acid (C₆H₃(COOH)₃), pyromellitic acid (C₆H₂(COOH)₄), pyromellitic dianhydride, trimellitic acid, trimellitic anhydride, trimethylol propane (C₂H₅C(CH₂OH)₃), ditrimethylol propane (C₂H₅C(CH₂OH)₂C₂H₄OC(CH₂OH)₂C₂H₅), dipentaerythritol (CH₂OHC(CH₂OH)₂C₂H₄OC(CH₂OH)₂CH₂OH), pentaerythritol (C(CH₂H)₄), ethoxylated glycerol, ethoxylated pentaerythritol (3EO/4OH and 15 EO/4OH from Aldrich Chemicals), ethoxylated trimethyol propane (2.5EO/OH and 20EO/3OH from Aldrich Chemicals), and Lutrol HF-1 (an ethoxylated glycerol from BASF).

[0037] Pentaerythritol is a preferred branching agent. Furthermore, if ethoxylated branching agents are used, experimental data suggests that use of polyethylene glycol having an average molecular weight of about 400 g/mol in weight fractions between about 4 percent and 15 percent provides excellent results. Applicant refers the reader to the above listed patents and applications for additional information regarding the amounts of branching agent that may be used.

[0038] As known to those familiar with the manufacture of polyester, the equipment used to spin polyester into filaments is designed, built, and adjusted to process polymers whose zero-shear melt viscosity falls within a certain range, typically between about 500 and 4000 poise. Thus, such equipment runs most satisfactorily when the melt viscosity of the copolyester is within this viscosity range. Accordingly, polymer compositions utilized in the practice of the invention should be polymerized until the viscosities of the compositions are suitable for commercial spinning. Additional information regarding viscosities of PEG modified polyesters may be found in U.S. Pat. Nos. 6,294,254; 6,303,739; 6,291,066; 6,322,886 and U.S. applications Ser. Nos. 09/801,853; 09/851,813; 09/444,192; 09/730,444; 09/761,446; and 09/827,441.

[0039] Referring now to FIG. 1, in one embodiment, the invention is a spinneret (4) having at least one opening (8) defined by a cross-section that is based upon an ellipse (10). The formal geometric definition of an ellipse is a curve for which the sum of the distances of any point on it from two fixed points (the foci) is constant. An ellipse (10), such as that shown in FIG. 1, may also be described in more general terms as an arcuate curve that is drawn around two perpendicular axes where the axes are of different length and bisect one another. Typically the longer of the two axes is called the primary axis (12) and the shorter of the two axes is called the secondary axis (14).

[0040] In a preferred embodiment, the opening (8) of the spinneret (4) is based upon an ellipse having a primary to secondary axes ratio of about 1.8 to about 2.9. Preferred lengths for the primary axis (12) are between about 0.3 mm and about 0.45 mm. Preferred lengths for the secondary axis (14) are between about 0.13 mm and about 0.22 mm.

[0041] The opening (8) of the spinneret (4) is further defined by a v-shaped notch (16) that extends from the perimeter of the ellipse (10) toward the interior of the opening (8). In preferred embodiments the v-shaped notch (16) is aligned or axial with the secondary axis (14); (i.e. the secondary axis bisects the angle formed by the v-shaped notch). The origin (18) of the v-shaped notch (16) is preferably located at a point on the secondary axis (14) that is between the outer perimeter of the ellipse (10) and the intersection of the primary (12) and secondary (14) axes. In a particularly preferred embodiment shown in FIG. 1, the origin (18) of the v-shaped notch is located at the intersection of the primary (12) and secondary (14) axes. As shown in FIG. 1, the v-shaped notch (16) is defined by an angle α. The angle α may be between about 35° and about 150°, preferably between about 45° and about 135° and most preferably between about 80° and about 130°.

[0042] Spinnerets having the following dimensions were shown to have favorable spinning properties and provide suitable filaments. In each of the following embodiments the origin of the v-shaped notch (16) was placed at the intersection of the axes. Primary Axis Secondary Axis Angle Primary Axis/ (mm) (mm) α Secondary Axis 0.326 0.176 90 1.85 0.362 0.158 90 2.29 0.406 0.142 90 2.86 0.346 0.188 120 1.84 0.386 0.168 120 2.30 0.43 0.15 120 2.87

[0043] The manufacture of non-circular cross-section filaments is often plagued by a phenomenon known as “kneeing”, which describes the sharp bend the filament makes as it leaves the spinneret and is quenched. It is thought that unequal velocity gradients caused by the non-circular cross-sections contribute to this phenomenon. In some instances the kneeing of the filament does not cause too much of a problem because all of the filaments leaving the spinneret knee in the same way. In other instances, however, a filament can bend and touch a neighboring filament causing a chain reaction that disrupts the entire spinning and take-up process.

[0044] Many spinneret packs are designed as an annulus where an annular spinneret plate has concentric rows of openings through which filaments are spun and brought into contact with a quenching medium (e.g., air). These types of packs often have a lip extending down from the interior wall of the annulus. If a filament knees too much it can touch the lip and disrupt the spinning process.

[0045] Kneeing has been observed in a few of the test runs using annular spinnerets such as those described above in conjunction with an annular quench of air. In a few instances the kneeing was sufficient to cause a filament to touch the annular lip of the spinneret pack. This problem was corrected by increasing the distance between the first ring of openings and the lip.

[0046] As foreshadowed by the above discussion regarding kneeing, a further embodiment of the invention comprises a method for forming a synthetic filament. The method according to the invention is shown schematically in FIG. 2. FIG. 2 is provided as a visual aid to the reader. Those skilled in the art recognize that each of the steps or components shown in FIG. 2 may be modified to achieve a particular result. Accordingly, FIG. 2 should not be interpreted as limiting the scope of the invention.

[0047] The method according to the invention comprises obtaining a polymer feedstock (20) of a fiber forming material. In the case of polyester, the feedstock (20) is typically in the form of a chip and is held in some type of storage device like a hopper (22). The polymer feedstock (20) is then fed to a heating unit (24) where it is heated to its melting point or above. The melted polymer is then fed via conventional means to a filter pack (26) and spinneret (28) having at least one opening (8).

[0048] The polymer is then forced through the openings (8) of the spinneret (28) to form a filament (6). The opening (8) is based upon an ellipse (10) having a primary axis (12) to secondary axis (14) ratio of between about 1.8 to about 2.9. In preferred embodiments the length of the primary axis (12) is between about 0.3 mm and about 0.45 mm. Preferred lengths for the secondary axis (14) are between about 0.13 mm and about 0.22 mm.

[0049] The opening (8) of the spinneret (4) is further defined by a perimeter having a v-shaped notch (16) that is generally aligned axially with the secondary axis (14). In preferred embodiments, the angle of the notch is between 35° and 150°.

[0050] The method according to the invention encompasses spinning filaments that are less than one (1) denier (microdenier) as spun. The method also encompasses spinning filaments that are and equal to or greater than one (1) denier as spun where the term “as spun” is used to describe the denier of the filament as it leaves the spinneret and before any subsequent drawing of the filament.

[0051] Those skilled in the art recognize that a single spinneret is capable of spinning filaments of several different deniers. The denier at which a material such as polyester is spun can be adjusted to some extent by adjusting the ratio of the filament's take-up velocity (i.e., the speed at which newly spun filament is collected on rollers) to its exit velocity (the velocity upon exiting the spinneret). In general, lowering the spinneret throughput and increasing the take-up speed will result in smaller denier filaments. Increasing the number of holes in the spinneret can also lower the deniers as spun. Care must be taken, however, because if the take-up velocity to exit velocity ratio becomes too great it can cause filament breakage.

[0052] Given the range of axes for the spinneret, a wide range of possible throughputs and speed ratios, a wide variety of “as spun” deniers are possible. Those skilled in the art are fully capable of sizing the spinneret and adjusting the take-up to exit velocity ratio to achieve both microdenier and multidenier filaments without undue experimentation.

[0053] The method according to the invention encompasses more than just the physical act of spinning a polymer melt through a spinneret. The invention also encompasses the steps of quenching the filaments and “take-up” of the filaments in which the quenched filaments are collected on a series of rollers for further processing or packaging.

[0054] Likewise, the method according to the invention includes drawing the filament and cutting the filament into staple fiber as is known in the art. The method according to the invention further extends to spinning yarns comprising the fiber of the invention. Yarns included within the scope of the invention include yarns made solely of the cut fiber and blended yarns that are comprised of the cut fiber and at least one other type of fiber. Possible fibers for use in spinning a blended yarn include cotton fibers, rayon fibers, acetate fibers, polypropylene fibers, nylon fibers, cellulosic fibers, spandex fibers, conventional polyester fibers, polylactic acid fibers, and copolyester staple fibers.

[0055] One of the benefits of the present invention manifests itself during yarn spinning. Yarns formed from fibers according to the invention have fewer ends-down during spinning as compared to ordinary circular fiber. Furthermore, the relative reduction in ends down tends to improve as the delivery speed increases. In short, the method according to the invention allows manufacture of yarns at higher speeds and with less breakage.

[0056] Test runs show that at a delivery speed of about 145 n/min, yarns formed from circular fiber had about 4 times the number of ends down as compared to yarns formed from the fiber according to the invention.

[0057] The reduction in ends down is a significant and unexpected improvement associated with the fiber according to the invention. More unexpected is that the improvement in ends down appears to apply across polymer types (i.e., PEG modified PET and standard PET). Although the Applicant does not wish to be bound by a particular theory, it is believed that the shape of the Applicant's fiber (possibly the subtle curve along one side) somehow improves the way the fibers bind together during spinning and directly improves spinning performance. One reason for looking to the shape of the fiber is that another surprising aspect of the invention is that the physical properties of fibers and yarns made according to the invention are almost indistinguishable from the physical properties of fibers and yarns incorporating standard circular cross-sections. This aspect of the invention is discussed in greater detail below.

[0058] The method according to the invention further comprises forming fabrics comprising the yarns and fibers of the present invention. Fabrics within the scope of the invention include woven, nonwoven and knitted fabrics.

[0059] Referring now to FIG. 3, the invention also encompasses a synthetic filament (6) having a cross-section based upon two axes of different length. The cross-section of such a filament is shown schematically in FIG. 3. FIG. 4 is a photograph of actual filament cross-sections that are on the order of 10 microns across their secondary axis. This particular size of cross-section is shown for demonstration purposes only and is not intended to limit the scope of the invention. As can be seen in FIG. 4 and confirmed in the following table, the filaments made according to the invention possess a high degree of uniformity. Accordingly, the filaments are described in geometrical terms such as “ellipse”, “perpendicular” and “bisect”. As used in the following table, the term “superimposed width” is a width measured by drawing a tangent line across the indention along one side of the filament (thus roughly completing the ellipse) and measuring the width of the filament from the midpoint of the tangent. The term % CV is the standard deviation divided by the mean. Uniformity of Filaments Superimposed Aspect Ratio dpf length actual width Width (Length/Super. (g/9000 m) (microns) (microns) (microns) Width) Average 0.92 14.4 5.8 6.6 2.5 Max. 1.20 16.6 7.3 7.9 2.3 Min. 0.75 13.0 4.6 5.3 2.9 Std. Dev. 0.10 0.9 0.6 0.5 1.6 % CV 10.40 6.4 10.0 8.3 0.6

[0060] The filament (6) according to the invention is defined in part by a primary filament axis (30) and a secondary filament axis (32) that generally correspond to the primary and secondary axes of the opening (8) of the spinneret (28). The axes are arranged perpendicular to one another and the secondary filament axis (32) substantially bisects the primary filament axis (30). The intersection of the two axes cuts the secondary axis into a first segment (34) and a second segment (36) where the two segments are of unequal length. In FIG. 3 the first segment (34) is shown as the shorter of the two segments.

[0061] The primary filament axis (30) divides the filament into a first portion (38) and a second portion (40) on opposite sides of the primary axis. The first portion (38) of the filament cross-section defines half of an ellipse.

[0062] The second portion (40) of the filament cross-section is defined by a curve (46) extending between the ends (44) of the primary axis (30). More specifically, the second portion (40) of the filament cross-section is defined by a curve (46) having a first convex section (48) and a second convex section (50) separated by a concave section (52) where the terms convex and concave are used in relation to the curves' relationship to the primary axis (30). The trough of the concave section (52) is defined by the end of the shorter of the two secondary axis segments (34).

[0063] In an alternative embodiment, the filament according to the invention is a synthetic filament with a non-circular cross-section that exhibits favorable properties in fibers, yarns and fabrics. The filament comprises a cross-section comprising an ellipse with one portion that is concave with respect to the primary axis of the ellipse. The concave portion of the ellipse is symmetrical about the secondary axis of the ellipse.

[0064] As noted in the context of the method and spinneret, the filament according to the invention may be made from any polymer capable of being spun into a filament and in particular includes condensation polymers selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate, poly(trimethylene terephthalate), other polyesters, PLA nylon 6 and nylon 66 or copolymers of any of these. Furthermore and as noted previously, filaments according to the invention also encompass polymers incorporating one or more additives or modifiers such as PEG, branching agents, delusterants, anti-static agents, colorants (e.g., dyes and pigments), etc.

[0065] Filaments according to the invention may be spun in deniers less than one (1) or equal to or greater than one (1) as discussed above. The filaments may also be drawn and processed into textile goods as is well known in the art. In particular, filaments may be cut into staple fiber that may then be used to form yarns. The invention includes yarns made solely from fiber according to the invention and blended yarns where at least one additional fiber in the yarn is selected from the group consisting of cotton fibers, rayon fibers, acetate fibers, polypropylene fibers, nylon fibers, spandex fibers, cellulosic fibers, PLA, biconstituent fibers, and conventional polyester fibers.

[0066] Yarns according to the invention may then be formed into woven, non-woven and knitted fabrics. The invention also encompasses fabrics made from filaments and fibers according to the invention.

[0067] As mentioned in the background section of the application, it is not uncommon (depending upon the particular filament) for non-circular filaments to possess physical properties that are markedly different to that of circular filaments (e.g., stronger or weaker). This is especially true with filaments of elongated cross-section. FIG. 5 is a plot of stress versus elongation for circular filaments and filaments according to the invention that were formed under substantially the same process conditions. FIG. 5 represents data obtained from polyethylene terephthalate filaments comprising low amounts of PEG (i.e. (2 weight %). Line A in FIG. 5 represents the performance of the circular filament and line B represents the performance of the filament according to the invention.

[0068] As can be seen from FIGS. 5 and 6, there is negligible difference in the stress performance of the filament according to the invention as compared to circular filament. This is beneficial because it means these filaments can be processed just like circular filaments.

[0069] The invention has been described in detail, with reference to certain preferred embodiments, in order to enable the reader to practice the invention without undue experimentation. However, a person having ordinary skill in the art will readily recognize that many of the components and parameters may be varied or modified to a certain extent without departing from the scope and spirit of the invention. 

That which is claimed is:
 1. A synthetic filament having a cross-section, said filament comprising: a primary axis and a secondary axis of different lengths, wherein said secondary axis bisects said primary axis, wherein said primary axis cuts said secondary axis into a first segment and a second segment where said first and second segments are of unequal length, wherein said primary axis defines first and second portions of said filament cross-section on opposite sides of said primary axis, wherein said first portion of said filament cross-section defines half of an ellipse, wherein said second portion of said filament cross-section is defined by a curve extending between the ends of said primary axis and having first and second sections convex to said primary axis separated by a section that is concave to said primary axis with the trough of the concave section being defined by the end of the shorter of the two secondary axis segments.
 2. A filament according to claim 1 wherein said filament comprises a condensation polymer.
 3. A filament according to claim 1 wherein said filament comprises a polymer selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, poly(trimethylene terephthalate), other polyesters, polylactic acid, nylon 6 and nylon
 66. 4. A filament according to claim 1 wherein said filament comprises polyethylene terephthalate.
 5. A filament according to claim 4 wherein said filament further comprises polyethylene glycol.
 6. A filament according to claim 5 wherein the weight fraction of said polyethylene glycol in said polymer filament is between about 2 percent and 20 percent.
 7. A fiber cut from the filament according to claim
 1. 8. A yarn comprising the fiber of claim
 7. 9. A yarn according to claim 8 wherein said yarn is a blended yarn further comprising at least one other fiber selected from the group consisting of cotton fibers, rayon fibers, acetate fibers, polypropylene fibers, nylon fibers, spandex fibers, cellulosic fibers, biconstituent fibers, polylactic acid, and conventional polyester fibers.
 10. A fabric comprising fiber according to claim 7 wherein said fabric is selected from the group consisting of woven, non-woven and knitted fabrics.
 11. A fabric comprising the yarn according to claim 9 wherein said fabric is selected from the group consisting of woven, non-woven and knitted fabrics.
 12. A filament according to claim 1 that is greater than 1 denier.
 13. A filament according to claim 1 that is 1 denier or less.
 14. A spinneret for spinning a synthetic filament, said spinneret having at least one opening, said opening based upon an ellipse having a primary to secondary axes ratio of between about 1.8 to about 2.9, said opening further defined by a perimeter having a v-shaped notch generally (axially) aligned with said secondary axis and extending toward the center of the ellipse.
 15. A spinneret according to claim 14 where in the origin of said v-shaped notch is located along the secondary axis.
 16. A spinneret according to claim 15 where in the origin of said v-shaped notch is between the outer perimeter of said ellipse and the intersection of said primary and secondary axes.
 17. A spinneret according to claim 15 wherein said origin of said v-shaped notch is at the intersection of said primary and secondary axes.
 18. A spinneret according to claim 14 wherein said angle of said v-shaped notch is between 35° and 150°.
 19. A spinneret according to claim 14 wherein said primary axis is between about 0.3 mm and 0.45 mm in length.
 20. A spinneret according to claim 14 wherein said secondary axis is between about 0.13 mm and about 0.22 mm in length.
 21. A method of forming a synthetic filament comprising: heating a fiber-forming material at or above its melting point; spinning the heated material through a spinneret having at least one opening, the opening based upon an ellipse having a primary to secondary axis ratio of between about 1.8 to about 2.9, the opening further defined by a perimeter having a v-shaped notch generally axially aligned with said secondary axis wherein the angle of said notch is between 35° and 150°; and spinning the heated material to form a filament.
 22. A method according to claim 21 wherein the fiber forming material is a condensation polymer.
 23. A method according to claim 22 wherein the condensation polymer is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, poly(trimethylene terephthalate), polylactic acid, other polyesters, nylon 6 and nylon
 66. 24. A method according to claim 22 wherein the condensation polymer comprises polyethylene terephthalate.
 25. A method according to claim 24 wherein the condensation polymer further comprises polyethylene glycol and a branching agent.
 26. A method according to claim 25 wherein the concentration of polyethylene glycol in the melt is between 2% and 20%.
 27. A method according to claim 21 wherein the filament is greater than 1 denier as spun.
 28. A method according to claim 21 wherein the filament is 1 denier or less as spun.
 29. A method according to claim 21 further comprising drawing the filament.
 30. A method according to claim 21 further comprising cutting the filament into staple fiber.
 31. A method according to claim 30 further comprising forming a yarn comprising the staple fiber.
 32. A method according to claim 31 further comprising forming a fabric comprising the staple fiber wherein said fabric is selected from the group consisting of woven, non-woven and knitted fabrics.
 33. A synthetic filament with a non-circular cross-section that exhibits favorable properties in fibers, yarns and fabrics, said filament comprising; a cross section comprising an ellipse with one portion that is concave with respect to the primary axis of the ellipse; and said concave portion being symmetrical about the secondary axis of the ellipse.
 34. A synthetic filament according to claim 33 wherein said filament comprises a condensation polymer.
 35. A synthetic filament according to claim 33 wherein said filament comprises a polymer selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, poly(trimethylene terephthalate), polylactic acid, other polyesters, nylon 6 and nylon
 66. 36. A filament according to claim 33 wherein said filament comprises polyethylene terephthalate.
 37. A filament according to claim 36 wherein said filament further comprises polyethylene glycol.
 38. A filament according to claim 37 wherein the weight fraction of said polyethylene glycol in said polymer filament is between about 2 percent and 20 percent.
 39. A fiber cut from the filament according to claim
 33. 40. A yarn comprising the fiber of claim
 39. 41. A yarn according to claim 40 wherein said yarn is a blended yarn further comprising at least one other fiber selected from the group consisting of cotton fibers, rayon fibers, acetate fibers, polypropylene fibers, nylon fibers, spandex fibers, cellulosic fibers, biconstituent fibers, polylactic acid, and conventional polyester fibers.
 42. A fabric comprising fiber according to claim 39 wherein said fabric is selected from the group consisting of woven, non-woven and knitted fabrics.
 43. A fabric comprising the yarn according to claim 41 wherein said fabric is selected from the group consisting of woven, non-woven and knitted fabrics.
 44. A filament according to claim 33 that is greater than 1 denier.
 45. A filament according to claim 33 that is 1 denier or less. 